Dangerous levels of powerful insecticides were found in two Norfolk rivers placing aquatic insects, fish and birds at risk, tests have revealed.

The River Waveney and River Wensum were two of eight rivers across England that were found to be heavily contaminated with neonicotinoid pesticides in tests conducted by the Environment Agency last year.

The Waveney was found to be acutely polluted while the Wensum, a Special Area of Conservation for its river life, was found to be chronically polluted.

Graham Elliot, Green Party councillor for Beccles North, said he was shocked by the revelations.

“I have always been quite proud of how clean our river is,” he said of the Waveney. “This is a serious worry to us all.”

Due to the harm they cause to bees and other pollinators, neonicotinoids were banned in 2013 by the European Union from use on flowering crops.

A vote to extend the ban to all outdoor uses is expected soon.

Tests for neonicotinoids in British rivers, as mandated by the EU, were conducted last year and the results recently released by Buglife, which is devoted to the conservation of invertebrates.

Chief executive Matt Shardlow said: “We are devastated to discover that many British Rivers have been heavily damaged by neonicotinoid insecticides.

“It is vital that action is taken to completely ban these three toxins, including in greenhouses and on pets, before another year of disgraceful pollution occurs.”

The Waveney and Wensum were two of 23 sites sampled in 2016 and Buglife said sugar beet fields were the most likely source of pollution in the Norfolk rivers.

NFU East Anglia Environment Adviser Rob Wise said the Environment Agency monitored water quality closely and the union was not aware of it raising any specific concerns about high levels of neonicotinoids in rivers.

“Farmers take their environmental responsibilities extremely seriously. They have high levels of pesticide stewardship through schemes such as the Voluntary Initiative, which offers advice and actions designed to keep crop protection products out of water.

“There is much specific work being undertaken by Norfolk farmers through the Broadland Catchment Partnership as well, including using new types of machinery in row crops such as sugar beet and potatoes, to minimise run-off into rivers.”